Freezing unit defroster



Juy 18, 1950 w. w. cowcalm.v

FREEZING UNIT DEFROSTER Filed June 18, 1947 ATTORNEY Patented July 18,1950 UNITED STATES PATENT OFFICE FREEZING UNIT DEFROSTER ApplicationJune 18, 1947, Serial No. 755,401

4 Claims. (Cl. 219-19) This invention relates to means for defrostingthe freezing compartment of refrigerators and so-called deep freezeboxes, and is particularly well adapted for use to release the layer oficeforining frost from the inner walls of a deep freeze box, so thatsuch sheet of ice may be lifted out of the box without the necessity ofraising appreciably the temperature of the food stored in the box.

When a freezing compartment is kept below the temperature at which waterfreezes the moisture in such compartment will deposit on the top, bottomand sides of the compartment and form frost. As this frost accumulatesit forms a layer of ice that, due to its insulating effect, reduces theefciency of the apparatus for reducing the temperature of the freezingcompartment. It is therefore necessary to defrost such compartment fromtime to time.

The general practice heretofore in defrosting the freezing compartmentof a deep freeze box has been to stop the supply of cooling fluid tosuch box and open up the lid of the box so as to expose the interior `ofthe box to room temperature and thereby cause the layer of ice upon thewalls to melt, but this practice is open to the objection that thetemperature of the food stored in the box rises unduly while the box isbeing defrosted. It has also been the practice heretofore to scr-ape thefrost free from the walls of the freezing compartment and then removethe scraping from the box, but this is a comparatively difficult job,and allows the contents of the box to become warm while this is beingdone.

The present invention contemplates a simple and practical freezing unitdefroster whereby the layer of ice-forming frost that has built up uponthe walls of the freezing compartment may be quickly and easily releasedfrom such walls and then lifted out of the box. This is accomplished byheating the wall itself or other surface upon which the ice-'formingfrost has become deposited so that this layer of ice will be released ordecemented from the wall upon which it formed and can then be lifted outof the compartment. In this manner the layer of ice-forming frost may beremoved from the interior of the freezing compartment in a short timeand without causing any appreciable rise in the temperature of the foodstored in the freezing compartment.

In order to carry out the present invention the walls, and also4 ifdesired the top and bottom, of the freezing compartment to be defrostedare each provided with a defrosting unit having the form of -a heatingsheet of substantial area which is secured to each wall that is to befreed from ice. This sheet-like heating unit may be adhesively securedto the exposed porcelain lined face of the walls of the freezingcompartment, or if desired it may be attached to the inner or concealedface of such walls against which the fibre glass or other insulatingmaterial normally rests.

The heating sheet, in accordance with the present invention, is soconstructed that it will generate heat approximately uniformlythroughout the entire area of the heating unit and is designed toproduce only a moderate amount of heat say about F. to 200 F. throughoutits area, since all that is required of such heating unit is to decementor release the bond between the sheet of ice and the wall of thefreezing unit to which itis adhered. As soon as this is done thereleased sheets of ice may be lifted out of the freezing unit in largesections.

The heating sheet used in carrying out the present invention comprises aplastic sheet having electrical conductivity, the desired amount ofconductivity is imparted thereto by employing .a plastic that containsconductive particles such as acetylene black. This permits an accuratecontrol of the heating properties built into the plastic sheet, sincethe conductivity of such sheet may be increased as desired by applyingthereto successive layers of a solvent plastic lm carrying theconductive particles. After a plastic sheet having the desiredconductivity is produced, electrical conductors preferably in the formof metal ribbons are secured thereto in spaced parallel relation to eachother, so that the conductor sheet will generate heat substantiallyuniformly throughout its area when a dierent electric potential ismaintained between the spaced conductors. The heating sheet thusproduced is preferably confined or sandwiched between two sheets ofinsulating material.

The above and other features of the present invention and novelarrangement of parts will be further understood from the followingdescription when read in connection with the accompanying drawingillustrating good practical embodiments of the invention, and wherein:

Fig. 1 is a perspective view of a deep freeze box having the four sidewalls thereof equipped with defrosting units in accordance with thepresent invention;

Fig. 2 is a perspective view of a defrosting unit of the type used inFig. l, and comprising an electrically heated plastic sheet;

Fig. 3 is a sectional view taken on the line 3 3 of Fig. 2;

Fig. 4 is a section view on an enlarged scale taken through one of theinner Walls of the deep Fig. l of the drawing shows in perspective vievra low temperature box of the type commonly referred to as a deep freezeunit or deep freeze box and is designated generally:bymthesntunenal.1it. This boxr has the usualflidll l`\sh'own\inizthe\ raised position sothat the interior ofthe* box-- which constitutes the freezingcompartmentmayl i These'tabs 23 provide a convenient means for conbeseen. The lid H is secured to the box lll by hinges not shown.

The walls of the box are made thi-cli as shown forheatinsulatingpurposesand '.corrrprisean outer.v

meta-lgshellfhavin'aithenoutei wallsirlzfandia.. con.siderablysmaller-.innermetal shell havingsthe'bottom: l andgside.;walls; l 4r. The..I arrangement is.r

suchcthat-.a hollow; space is-.lefitibetween the.- inner. and outeryshells :,which; isiilfled'.; with bre .glass or otherI heat; insulatingmateriaL. not: shown. Theyinner; and outerL shells.. justy mentioned.yare connected atzthe upper.. end of'. the boxlby the.

nolinedmetal; wallsil 5: which' slope. torcorrespond Withithebeveloithe; thiclciinsulating. portion known .construction iandconstitutesone form. ofV

freezingiunit which mayibe: readily,l equipped with the.; defrosting.uifiits contemplatediby .the present invention. One; such @frosting unitdesignated, by i8 is shown in perspectiveninsliigs,2;.of; thelIfvilfililehz Thisl vunit, may@l bei applied ...to'all `four vertical gwallsxv l 4': of the., innerqshell .off the. dee

freeze;unit, and ,if desired .-it may also, be. applied. to the bottomi3 and .to the. surface.vv lsof the lid i i, however: it;is;shown inFigs Al as. having been..

applied onlyitofthe-fon-r .Walls l 4l:

The heating; uniti. 84, preferably, comprises. a,

sheet` I9, seef` Fig,4;, hai/ing; electrical; conduce tivity,;, a-ndthis sheet is sandwiched between ,two non-conducting-Vsheets 2D,and 2i.VThesheetl.

.50. fabric, such asiondinaryrwoveni,cotton fabricoor..

preferably fisA formedaof. ag, sheeti of. thin Lwoven i \J- ofthefl-idIl... Thefbevelfledzportioni of thebox. iii-:has secured thereto.-th'e.I rubbersealing bead'l'i,A

The deep freeze..:,box:;so. far describedis ofwell...

a sheet'oftough durable-paper, ,and has applied to. one, face.thereofiaaplastic lm carrying,- electrical,conductiverptoperties.. Thisnlm Iis. preferably formed of rubber, and is appliedrto the fabric. or`paperv as .-a thin solvent coating having ofthe same .textile `fabric orpaperas is employed; in the sheet i9 and are coated with a'solventvresin such for example as a phenolic resin or polystyrene. Theinsulating sheets 20 and,v 2 i are slightly larger in area thantheconductive sheet i9 so that the insulating sheetsfwilhextend beyondthe four edges of the conductive sheetto completely insulate itasfshownin Fig. 2.`

In order to supplythe conductivesheetl 9 vwith an operating electricalcurrent `it has` placed lengthwise thereof .adjacent itsopposite edges,as

shown in Figs. 2 and 3, the tape conductors 22.

4 formed of thin strips of metal such as aluminum or copper. After theparts are assembled in the position in which they are shown in Figs. 2and 3 the composite sheet thus produced with the conductive tapes 22 inplace is preferably placed in a heated platen press, whereupon the pressis closed for a suiiicient length of time to soften the lplastic coatingon the sheets 2G and 2l and bond the several parts rmly together,- tothereby provide the finished heating unit having a thickness of onlyseveral hundredths of an inch. This completes the formation of theheating unit I8 exceptith'at contact tabs 23, shown as of the eyelettypeVare-preferably.secured to one end of each of theconduct-or=stripg-22 as shown in the drawing.

.Y enamel layer is designated.by'r MisimFigsA and 5 `of,- the. drawing,whereasthe: oppositeiaface of.: the`r Wall i4 which isf. normally gconcealed; and L. against. which. the.-insulating material..commone1y.restseisidesignatedzby. |45. intthese;itwoiguresr..

The; enamelacoveredzfaeesi 2.4!:y ofrtheiverticall walls l4,;.when,the-.z freezing; unit isin..operation. to. c keep.;y the..` food.thereinir. frozen',- arei: ther.wal-ls, upon whichiiceeformingfifrostaccumulates:4v As*` this frost increases in thicknessrit.forms;:a.;heattinsulating layerr. that aseriously' interferes with the. zefficiency;of.; the 'boimtosmaintain i ther-freezes.v

ing compartment i. at\T thee .desired r low. tempera-.f ture,whi.ch.in-.most cases should ybe ;around. zero i Fahrenheit., Itris;1therefore. important'.v to..v de-s frost; ther deepj freeze vunit-lfrom'. time; toi times., say.. at.l least .onceisinzthnee monthsp. butiAif a the.;E

freezing uidto theeboxsis -.cutpoff and itheelid is zleft openisoL-thatithe `vfreezing; compartmenti. becomes. warnrxenoughetormelt.: the ,i icedeposited n uponsuchs walls;J ,theI frozen'.: food: stored;` in: then,box :.is, likely. to..spoitidueztogitsfrisesin;.texnperaer ture..

Having in mind the dilcu-ltyiemaerencediflfiereej tofore indefrostingrthei-freezingtcompartmentnot;

freezing unitS.- thee presenti inventiorrzbonteme plates the userl of sa; defrosting., unit .comprisingf.

the; heating-sheet I 8,.;best-:sh1ownginiFig-...2 lof the.: drawing, andwhichisheetfisiused nponaeaclnwalli of ,theibox or othenfreezing'eunit,tdzbe -defrosteda `It will.lgiioted; that" each; ofi the .foumvertical.

Walls lll f, of: thesbox lihas secured; thereto: as heatingmnitl 8i thatis;` large enough itoicoyer sube ,Y stantially theeentiregarea ofiithewallrlll. to which;

it'is secured.V Theeheatngaaunit; ISeniayrbe.fape:`

p1ied;. to ithenenam'el ifacec 2.4.-

each:` Walle] 4 as i. shown,y in.. Fig-:i.4-i'of1'theidrawing.. or it1:. may. bei. applied;;to;the innen concealedzfacex l 4if'ofi. said iwalls-asl shown inggFigs, 5mt-the drawngr.. In.;

either; case iti wille serve to generates.sumcient;n

heat throughout.; its .entirei areae. toerelease ion decement.theebond'i which* securesV theialayer of iceto` such ;w,all.v Asesoonassthislfis.:.donau-thetintegralilayerV office, .,or;`aalarge:portion-.of sucha:V layer which'isi-now..:releaseils fronmawalnut-main berlifted-bodilyyout ;ofthe .-boxe., Asgaaresult thea mates.

defrosting of the box may be carried out quickly withoutjthe temperatureof the )frozen food stored' inthe box rising appreciably, since the icein the lbox-does not have to'be melted vbeyond the-point where its bondto the Wall I4 is releasafed.-l Due to the high vh eatinsulatingpropernesy of the'lfrost ice the heat'appiied to the box wallswill be conned to thefvicinity of such walls bythe Alayer of icedeposited thereupon -and will not raise the temperature of the storagespace appreciably.

The heating unit I8 may be secured to the enamel face 24 or to theinnerface I4 of a Wall I4 by simply Aadhesively bonding it to such wallto cover a large area thereof.

In the construction shown in Figs. 1 and 4 the ice-forming frost will bedeposited on the exposed iace of the heating unit I8 rather than uponthe wall it covers, so that when the heating unit is supplied with aheating current the ice will quickly release its grip upon the outerface 2D of the heating unit. On the other hand if the heating unit issecured to the inner face I4 of the wall I4 as shown in Fig. 5 of thedrawing and current is supplied to this heating unit, its heat will bequickly transmitted through the wall I4 to cause the ice deposited onthe enamel face 24 to release its hold.

In some cases it may be desirable to avoid the expense of applying theenamel 24 to the walls I4, and in place thereof apply the heating unitsI8 directly to the metal face of the walls I4, and then cover the entireinterior of the box with a protecting iilm of polystyrene so that itwill cover the pads I8 and exposed portions of the walls I4.

If the heating unit is applied to the face I4' of the wall I4 as shownin Fig. 5, the problem of supplying operating current to the conduc tivestrips 22 is a simple one, since all that is necessary is to connect oneconductor wire 25 of an insulated conductor 26 as shown in Fig. 5 to theupper tab 23 of each heating unit I8, and a similar conductor 25 to thecorresponding lower tab 23 of such heating unit.

When the heating unit I8 is applied to the enamel face 24 of the wall I4as shown in Figs. l and 4 it is then preferable to form a hole throughthe wall I4 at each point where a tab 23 is positioned so that each tabmay be connected with a conductor wire 25 of an insulated conductor 26disposed adjacent the inner wall I4. One construction for connectingsuch tab with a conductor wire is shown in Fig. 4 and comprises a stud21 which is tightly secured in an insulating sleeve 28, which sleeveextends through a hole formed in the wall I4. This stud 2l is internallythreaded at one end to receive the screw 29 which is employed to clamp atab 23 to the outer end of the stud 21. The inner end portion of thestud 21 has mounted thereupon the insulating disk 30 and the clampingnuts 3| to clamp between such nuts the conductor wire 25. In theconstruction of Figs. 1 and 4 the head of the screw 29 may be paintedover with shellac or other insulating material, and the clamping nuts 3land other exposed portion at the inner end of a bolt 2l may be coveredwith suitable insulating material. Likewise in Fig. 5 an insu latingsheet 32 is preferably provided between the tab 23 and the wall I4, andthe parts 23, 25 may be further protected by insulating material notshown. The insulated conductors 26 are the positive and negative Wiressecured to the tabs 23 to operate each heating unit I8 and are ledinwardly 'from the cable 33 that i enters a yhole i in a lWall of theIbox. Thiscable- 33 mayb'e con-v 'l nected `tothe ordinary volt outletbox.

It will be understood thatthe heating units I8 may beapplied also to thebottom I3 and top'IB of the box I0; but the application of the heating`unit I8 to the four upright'v walls I4 will` enable' the box tobequickly freed from the most objectionable vdeposits of ice within thefreezing'comy partment. It is desired to point out that while;

the freezingi unit defros'terf of the present invention has been shownand described in connection with a deep freeze unit, it is also Welladapted for use in defrosting the low temperature `compartment of theordinary household refrigs,

erator, and for use to defrost various other types of low temperatureboxes having a freezing compartment provided with walls upon which alayer of ice-forming frost tends to accumulate.

Having thus described my invention, what I claim and desire to protectby Letters Patent is:

l. In a low temperature box having a freezing compartment, top, bottomand side Walls enclosing said compartment and upon which a layer ofice-forming frost tends to accumulate, a defrosting unit comprising aflexible heating sheet adhesively secured to one face of at least one ofsaid walls so as to cover a large area of such face and heat this areaapproximately uniformly to free it from the layer of ice, including aplastic sheet having electrical conductivity and spaced current supplyconductors attached thereto so that this sheet will generate heatsubstantially uniformly over its surface when a difference in electricpotential is maintained between said conductors and heat the wall towhich it is secured.

2. In a low temperature box having a freezing compartment, four uprightwalls enclosing said compartment and upon which a layer of iceformingfrost tends to accumulate, a defrosting unit for each wall comprising aflexible heating sheet adhesively secured to one face of each of saidwalls so as to cover a large area of such face and heat the areaapproximately uniformly to free it from the layer of ice, including aplastic sheet having electrical conductivity and spaced current supplyconductors attached 'thereto so that this sheet will generate heatsubstantially uniformly over its surface when a difference in electricpotential is maintained between such conductors and heat the wall towhich it is secured.

3. In a low temperature box having a freezing compartment, wallsenclosing said compartment and upon which a layer of ice-forming frosttends to accumulate, a defrosting unit comprising a laminated heatingsheet adhesively bonded to at least one of said walls so as to cover alarge area of this wall and heat this area approximately uniformly torelease the layer of ice formed upon such sheet, including a plasticsheet having electrical conductivity and spaced current supplyconductors attached thereto so that this sheet will generate heatsubstantially uniformly over its surface and heat the wall to which itis secured when a difference in electric potential is maintained betweensaid conductors, and an insulating layer covering the heating sheet.

4. In a low temperature box having a freezing compartment, wallsenclosing said compartment and upon which a layer of ice-forming frosttends to accumulate, a defrosting unit comprising a heating sheetadhesively secured to one face of a wall of such compartment so as tocover a large area of such wall and heat this area.approxielectricakconductivityj and spaced conductors ail-1 5 1,815,324;1,974,146 235mm.Y 2,321,5s7t 2500168 Number

